GNU bug report logs -
#36597
27.0.50; rehash hash tables eagerly in pdumper
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Reported by: Pip Cet <pipcet <at> gmail.com>
Date: Thu, 11 Jul 2019 14:07:02 UTC
Severity: normal
Tags: patch
Found in version 27.0.50
Done: Paul Eggert <eggert <at> cs.ucla.edu>
Bug is archived. No further changes may be made.
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Message #17 received at 36597 <at> debbugs.gnu.org (full text, mbox):
On Sun, Jul 14, 2019 at 3:49 PM Paul Eggert <eggert <at> cs.ucla.edu> wrote:
> Pip Cet wrote:
> > Indeed, that's plenty of small Emacs processes not doing very much.
> > It's not the case we ought to be optimizing for, I think, but the
> > performance concerns should be taken seriously.
>
> What's a good benchmark for what we should be optimizing for? Ideally something
> somewhat-realistic as opposed to a microbenchmark.
I'd suggest something along the lines of:
perf stat -r 10 --table -e
cycles:u,instructions:u,branches:u,branch-misses:u make -B
../lisp/leim/ja-dic/ja-dic.el
With my patch:
61,136,837,192 cycles:u
( +- 0.42% )
42,313,912,525 instructions:u # 0.69 insn per
cycle ( +- 0.00% )
12,131,893,779 branches:u
( +- 0.00% )
47,602,747 branch-misses:u # 0.39% of all
branches ( +- 1.11% )
without my patch:
61,460,927,899 cycles:u
( +- 0.44% )
42,358,289,131 instructions:u # 0.69 insn per
cycle ( +- 0.00% )
12,134,582,441 branches:u
( +- 0.00% )
48,540,232 branch-misses:u # 0.40% of all
branches ( +- 1.09% )
A 0.5% improvement.
By comparison,
perf stat -r 100 --table -e
cycles:u,instructions:u,branches:u,branch-misses:u
~/git/emacs/src/emacs -Q --batch
With my patch:
80,749,425 cycles:u
( +- 0.81% )
146,770,045 instructions:u # 1.82 insn per
cycle ( +- 0.00% )
29,218,226 branches:u
( +- 0.00% )
450,275 branch-misses:u # 1.54% of all
branches ( +- 0.11% )
without my patch:
78,896,395 cycles:u
( +- 0.12% )
147,059,777 instructions:u # 1.86 insn per
cycle ( +- 0.00% )
29,287,917 branches:u
( +- 0.00% )
450,194 branch-misses:u # 1.54% of all
branches ( +- 0.09% )
About a 2% slowdown.
perf stat -r cycles:u,instructions:u,branches:u,missed-branches:u
> is dominated by a single CPU-intensive Emacs process and takes about 19 CPU
> seconds on my home desktop. The proposed patch slows this benchmark down by
> about 0.6%. (I ran the benchmark ten times after a warmup run, and took the
> average of the ten user+system times.)
Hmm. I'd like to know the reason for that, but I suspect it may simply
be thermal throttling. That's the reason I'm running tests in
parallel, though it might be better to compare instruction counts or
scheduled ยต-ops rather than cycles...
This bug report was last modified 4 years and 284 days ago.
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